Castle in the Sky
by DragonWolfStar
Summary: In which Castiel tries to do the right thing, Tony is no longer the smartest guy in the room, and Steve adjusts. Can be read as a Standalone. Sequel to 5 Times Cas Helped Steve


A/N: Pre AoU, mid-season 10 for SPN. Sequel of sorts to 5 Times Cas Helped Steve, but can be read as a standalone.

...So this was going to be funny. Instead it got hit by the feels train. Uh, happy reading?

"Wait," Tony says, expression of pinched disbelief warring with the budding excitement in his voice. "Wait. Time travel. As in, actual, take a quick jaunt to the time of the dinosaurs type time travel."

And, oh, there was no way this could possibly end well. There were a dozen reasons Steve could come up with off the top of his head that made the combination of Tony and Time Travel a horrible, potentially terrifying, combination.

Not to mention, there was not a single Avenger who understood what was going on with Cas and his grace. As far as Steve knew, it wasn't even his. It would be impossible.

That didn't stop Tony from all but leaping in excitement at the angel's reply.

"Yes," he said, bemused. "Though such an undertaking would be extraordinarily difficult. Going back for such a span of years would be next to impossible for anything short of an archangel."

Tony waved that apparently insignificant matter aside. "But how does it work? There are dozens of theories about the nature of time travel. Like the grandfather paradox," he said, words almost running together in his eagerness. "You know, if you went back in time, killed your grandfather, then you wouldn't be have been born to go back and kill him." Steve was forced to duck as one of Tony's hands nearly swatted him as he spoke.

Castiel frowned. "I do not understand humanity's repetitive desire to murder their grandrathers," he said flatly, and Steve smiled. It was hard not to be amused by Castiel's ability to take everything extremely literally.

Tony's jaw worked soundlessly for a moment before he muttered, "They don't actually want to... It's just an potential situation used as an example to describe... you know what? Nevermind."

Plus, Steve would admit, watching Tony flounder for a response was always funny. Castiel's lack of pop culture knowledge made most of Tony's snappy comebacks fall flat. That Steve could feel some smug satisfaction over that (he was sure it was some kind of karmic retribution, for all the engineer's jokes on Steve and Thor's behalf) was besides the point.

Castiel still looked confused, but seemed willing to let it slide. "Very well. Concerning the nature of traveling backwards in time, the closest answer I can give you using your terminology would utilize a number of partial differential equations..."

Tony raised a hand. "JARVIS, make sure you're getting this."

"Indeed, sir."

He gestured at the angel. "Onwards, McFly."

Castiel's frown deepened. "I am not-"

Tony cut him off, visibly restraining an exasperated sigh. "Continue, please."

"Very well."

Steve caught very little of the following conversation despite the fact that he heard every word. While he'd been no slouch in school, this was so far over his head he wouldn't even know where to begin. He shook his head, flipping his sketchbook open and wondering idly what to draw. He had only just started sketching out a cartoon when something caught his eye.

At some point, the inventor had brought out a tablet and the duo had begun using it to project a series of equations for Tony to look at. The soft light from the holographs cast a faint blue glow on the three, but ther seemed to be an extra glimmer coming from the engineer. Steve blinked at it.

Tony was sweating.

The tiny droplets glistened faintly blue, and Steve realized he hadn't heard Tony speak for several minutes now. Castiel's rough voice had faded to a low drone, a soothing, uninterrupted constant in the background.

Anyone who had ever met Tony (and quite a few people who hadn't) knew he wasn't a quiet person. Even at his most bored, Tony always had something to say. Now though, his jaw was clenched shut, eyes practically boring holes into the numbers and symbols floating above the tablet. His brow was furrowed, finger twitching restlessly on his thigh.

He didn't say a word. Not a single exclamation or question passed his lips.

Steve watched for a solid minute as Tony's expression grew more and more pinched. He could all but see well-oiled gears grinding to a halt because, for all his vaunted intelligence, he had nothing.

Tony was confused. He was looking at math, at physics, at all the things he was good at, and he couldn't comprehend a damn thing.

Steve choked just a bit. Castiel blinked, turning to him in askance. "Yes?" he asked, in-depth explanation paused for the moment. Steve waved off the question, still looking at Tony.

The inventor didn't move. Tony appeared frozen, even his agitated twitching stilled as he attempted to stare the equations into divulging their secrets.

"Uh, Tony?"

The soldier and the angel both waited. Nothing.

Steve reached forward, gently tapping his friend on the shoulder. Aside from a gentle sway, there was no reaction. He turned to Castiel. "I think you broke him."

Castiel's head tilted as he studied Tony in apparent fascination and concern. Possibly wondering why the man wasn't functioning at optimal parameters.

The engineer chose that moment to let loose a high-pitched whine from the back of his throat.

"Tony?" Steve repeated.

"Are you well?" Castiel asked.

"What? No. Yes. I mean yes. Math. Um, Steve, Cas. Look. I just realized, people to do, things to see. I'm going to be really, really busy for the next... month... or so. Later."

He hightailed it, booking it out the door so fast Steve was afraid he'd hurt himself on the way out. A moment later he swept back in, grabbed the tablet, and was gone again.

Steve and Castiel traded a look.

Well. This should be interesting.

o0O0o0O0o

Steve didn't see Tony for a solid week. He suspected it would have been even longer but for the fact that Bruce and JARVIS double-teamed him into going to Tony's lab himself. JARVIS, he could understand. The lack of opposable thumbs occasionally did make it difficult for the AI to watch out for his maker. Bruce though? Steve sighed, knocking sharply on the glass next to the door even as it slid open.

He stopped as his eyes took in the numerous floating equations. Some had glowing lines slashed through them; others were marked in a rainbow of colors, some strange organizational system Steve couldn't hope to understand.

In the middle, there was Tony, red-eyed and muttering to himself, hands alternately swiping away numbers and writing more.

Castiel was there, eyeing the inventor in quiet concern even as he pointed out another error in Tony's calculations.

Steve was suddenly acutely aware of why Bruce had left this to him.

"Cas," he greeted dryly. This was going to be one of those times, he knew, when he had to explain to the angel the subtleties of human behavior. "Can we talk?" He wondered absently when angel-education had been left to him, since these situations always seemed to end up with him being volunteered in one way or another.

For once, the angel appeared to know why Steve wanted to speak with him. "He was distressed. I had thought helping him to understand would make y-him... happy."

Steve winced, taking in the clear signs of a week-long manic mathematic binge. "It probably would," he acknowledged, "if he were capable of it." This was just one of those things humans likely weren't meant to understand, he was sure. (He might have even been a bit relieved - again, Tony and time travel together was something he just didn't want to contemplate.

"Wait," Steve stopped, frowning down at the angel. "What were you about to say?"

Castiel looked away. Steve could acknowledge that he was a bad liar, but Castiel's control over his vessel's expressions made the angel truly abysmal at it. "I don't know what you mean."

Steve leveled a stern look at the angel; the one that always caused Colonel Philips to groan aloud because it meant Steve was getting his way and damn the consequences.

Castiel deflated. "I thought this would make you happy," he murmured, eyes downcast. "I cannot do this myself, and Tony seemed interested."

Steve's mind blanked for an instant, breath hitching softly. He would be lying if he said the thought hadn't thought of it before. For several heartstopping moments, he'd given serious consideration to the idea of going back, of seeing Peggy, saving Bucky.

But not only was that impossible, as Cas no longer had his wings, Steve was absolutely certain it would be the wrong thing to do. As much as he still longed for his old life, he couldn't find it in himselft to give up his new one. Going back for an uncertain chance at saving his friend, stoping Schmidt, loving Peggy? Maybe things weren't perfect now, but there was no guarantee he wouldn't make things worse.

Peggy had lived her life, Red Skull was dead, and had been given a second chance in the form of the Winter Soldier. He had the Avengers, he had Sam and Cas, and he had a mission. Asking for more would be beyond selfish.

He glanced around the lab. And, of course, there was this.

"Cas," he said gently, voice coming out slightly hoarse, "I appreciate it, I really do. But this? I couldn't..." the soldier swallowed, taking a moment to collect himself. "Giving Tony a minor breakdown is really not the way to do it," he finished finally, trying to inject some humor into his voice and falling flat.

Tony abruptly spun around, lips pursed. "It wasn't just him. You..." he stopped, sighed, and waved. The holograms winked out of existence. "You don't smile. The happiest I've seen you is when your crazy assassin friend makes a big enough splash for you to follow. We can't replace what you had, we get it. But what we can do, is this," he said, arms sweeping around the room littered with empty coffee mugs and scribbled notes.

Steve could hear the underlying message clear as day. We aren't enough for you. He fought back a grimace, because that wasn't it. That wasn't it at all and he'd been grieving, and seeing Bucky again had brought back a lot of issues he'd been steadily ignoring until now, but that Castiel, let alone Tony, could think they weren't doing enough was wrong.

So Steve squared his shoulders and wracked his brain, letting the corners of his lips twitch up as he came up with something appropriate.

"Slow down there, Terminators," he said dryly, and it sounded beyond awkward but had the desired effect as Castiel tilted his head and Tony gawked. "Thank you, really, but... it's not. It's not necessary."

"If there is one thing I have learned from Dean and Sam, it is that if you have a chance at happiness, you should not squander it. Such moments may be fleeting, but yours is not as gone as you would think." Castiel's piercing blue gaze met Steve's. "You don't wish to go home?"

Steve looked at them, thought of the Avengers, of Sam and Cas and of the Winter Soldier, out there somewhere for Steve to find.

"I am home."

o0O0o0O0o

Castiel had taken Steve at his word, and tried his hardest not to further incite Tony's interest in the subject. He'd left the Tower to return to his own mission with a solemn promise to keep safe, and to return when he could.

And Tony... well, if the sudden dip in their coffee reserves was any indication, was learning a whole new method for using math. So when, a few days later, Tony stalked upstairs all but growling as he hunted for a source of caffiene, Steve just smiled.

"Going well?" he asked in amusement.

The glower Tony leveled at him was well worth it, he mused. He knew a few people who'd probably get a kick out of the continuing, sheer frustration emanating off the inventor and the only math he hadn't been able to solve. He'd let them know.

But the next time he saw Bucky or Cas, he'd have to remember to tell them just one thing more.

Welcome home.


End file.
